Combining a battery energy storage system (BESS) and a hydropower unit to provide primary frequency control has been researched in recent years due to the perceived benefits for both turbine and BESS operation. However, control algorithms and storage sizing recommendations for such a system remain scarcely published topics, with results derived from simulation models and lacking verification from field data. In 2019 Fortum installed a 5 MW and 6,2 MWh BESS at one of the 25 MW turbines in the Forshuvudforsen hydropower plant in Sweden. Operational data of the hybrid system providing frequency control is presented and analysed in this paper. A simple hydropower and BESS model, used in similar studies in literature, is compared to the obtained data, showing high accuracy for the hybrid system power output. This verifies that the model can be used for FCR provision design and power system studies. Although the standard hydropower unit model is not able to capture all the dynamics present in the measurements, comparison to data shows that the model is able to closely replicate the turbine wear and tear reduction and estimated BESS lifetime for hybrid operation.